Ten male volunteers without histories of drug abuse, except for cigarette smoking, were tested to assess the possible adverse performance effects of a cholinomimetic and a cholinergic antagonist, each given alone and in combination. A dose run-up procedure was employed in which physostigmine was administered i.v. in an ascending dose series (0.25, 0.5, 1.0, 1.5, and 2.0 mg) first alone, then following pretreatment with 5.0 or 10. 0 mg of methscopolamine, a peripherally active antagonist. Methscopolamine was given to assess the degree to which peripheral blockade reduced physiological effects and/or performance impairment. The Army Performance Assessment Battery (PAB), including components of the Triservices PAB, was used to evaluate behavioral performance. Preliminary analyses are ongoing.